This invention relates to a superconductive Josephson circuit device adapted to shift a flux quantum as an information bit from one superconductive quantum interference loop to another superconductive quantum interference loop by magnetically series-connecting a plurality of superconductive quantum interference loops each having a Josephson junction.
U.S. Pat. Nos. 3,626,391; 3,281,609; 3,758,795; 3,825,906, etc. disclose the concept of utilizing a Josephson junction for Josephson circuit devices as, for example, a memory cell, logic gate or shift register. Such a shift register is shown as comprising a parallel circuit of a first superconductive line including a single Josephson junction and a second superconductive line having a series circuit of an inductive element and resistive element, in which the second superconductive line of a preceding stage is arranged close to the Josephson junction in the first superconductive line of a next subsequent stage so as to obtain a magnetic coupling therebetween. Such an arrangement is called "a current-steering circuit". A control current feeding line is disposed adjacent to the Josephson junction in the first superconductive line. When control current above threshold flows through the control current feeding line, the Josephson junction switches from no voltage state to finite voltage state to permit flowing of current on the second superconductive line. If the current on the second superconductive line which is controlled by such a switching operation corresponds to control current on the above-mentioned control current feeding line, it can be used as control current to the Josephson junction in the first superconductive line of the next subsequent stage to permit sequential shift of the finite voltage state. The circuit arrangement including the above-mentioned Josephson junction, however, involves a great power dissipation, because a voltage on the Josephson junction is long continued. Furthermore, the time for the Josephson junction to be returned to no voltage state after such a finite voltage state has been attained requires more than 10 times as large a time as required when the Josephson junction is switched from no voltage state to a finite voltage state, thus making a required time for binary circuit operation prominently unbalanced. As another example can be listed a superconductive device called "a flux shuttle" which performs a similar operation to a shift register. Such a concept is already disclosed in U.S. Pat. Nos. 3,676,718; 3,936,677, etc. In such a flux shuttle arrangment, two superconductor layers are superposed with an insulating layer for tunneling being interposed therebetween in which insulating layer is make sufficiently thin to permit tunneling of electrons. A Josephson junction is provided in a transmission line form and a bias current source is provided which supplies a bias current between the superconductors. A plurality of control current terminals are provided at predetermined spacings on one of the superconductors. With a DC bias current being supplied from the bias current source, a control current is sequentially supplied in a periodic fashion and a vortex created in the Josephson junction is moved, while trapping a flux quantum, along the Josephson junction transmission line. The flux shuttle arrangement serves substantially as a shift register.
Since, however, the flux shuttle is such that the Josephson junction is formed uniformly over its wide area, it is difficult to manufacture in good yield. When an attempt is made to obtain a high packing density by reducing a spacing required to form one vortex, it is necessary to particularly make a tunneling current density very high and in consequence the insulating layer for tunneling very thin. This provides restrictions to the manufacture of flux shuttles. Where a logic gate such as an AND circuit and an OR circuit is constructed with the flux shuttle arrangement, the Josephson junction transmission line is bifurcated to permit the direction of movement of such a vortex to be controlled. To this end, it is necessary to supply a different control current to each bifurcation according to the function. As a result, a control circuit required for the control of the vortex is made complicated.